• Elastomers and Composites
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• v.57 no.4
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• pp.165-174
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• 2022

The effect of fumed silica loading on the thermal stability and mechanical properties of fluorosilicone (FVMQ) rubber was investigated. The distribution of fumed silica inside FVMQ was characterized using scanning electron microscopy, and the thermal stability of composites was evaluated using thermogravimetric analysis and by the changes in mechanical performance during thermo-oxidative aging. The function mechanism of fumed silica was studied by Fourier transform infrared spectroscopy. The results show that with increasing silica content, the crosslink density of composites, the modulus at 100%, and tensile strength also increased, whereas the elongation at break decreased. Furthermore, increasing the silica content of composites increased the initial decomposition temperature (T_d) and residual weight of the composite after exposure to nitrogen. In addition, the thermal oxidative aging experiment demonstrated improved aging resistance of the FVMQ composites, including lower change in tensile strength, elongation at break, and modulus at 100%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.9
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• pp.915-923
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• 2007

Rubber hoses for automobile radiators are apt to be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under thermal and mechanical loadings. The aging behaviors of the skin part of the hoses due to thermo-oxidative and electro-chemical stresses were experimentally analyzed. Through the thermo-oxidative aging test, it was shown that the surface hardness IRHD(International Rubber Hardness Degrees) of the rubber increased with a considerable reduction of failure strain as the aging time and temperature increased. On account of the penetration of coolant liquid into the skin part influenced by the electro-chemical degradation(ECD) test the weight of the rubber hose increased, whereas their failure strain and IRHD hardness decreased. The hardness of the hose in the side of the negative pole was the most deteriorated at the test site of the hose skin just below the coolant surface.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.5
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• pp.368-376
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• 2005

Coolant rubber hoses for automobile radiators can be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under thermal and mechanical loadings. In this study, for EPDM(ethylene-propylene diene monomer) rubber conventionally used as a radiator hose material the aging behaviors of the skin part due to thermo-oxidative and electro-chemical stresses were nondestructively evaluated. Through the thermo-oxidative aging test, it was shown that the surface hardness IRHD(International Rubber Hardness Degrees) of the rubber increased with a considerable reduction of failure strain. On account of the penetration of coolant liquid into the skin part the weight of rubber specimens degraded by electro-chemical degradation(ECD) test increased, whereas their. failure strain and IRHD hardness decreased largely. The penetration of coolant liquid seemed to induce some changes in inner structure and micro hardness distribution of the rubbers. Consequently, EPDM rubbers degraded by thermo-oxidative aging and ECD could be characterized nondestructively by micro-hardness and chemical structure analysis methods.

• Composites Research
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• v.22 no.3
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• pp.35-43
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• 2009

In this study, for a radiator hose made of carbon black filled EPDM(ethylene-propylene diene monomer) rubber, a measuring method of crosslink density was established to analyze the aging behaviors under thermo-oxidative stresses. At $125^{\circ}C$, the crosslink density of the rubber specimens decreased slightly in the initial stage, but increased with increasing the aging time. Such variation in crosslink density was similar to that of tensile strength. This might be due to the formation of sulphoxide crosslinks as well as to additional crosslinks made by the reaction of unvalcunized sulfurs. A high temperature aging of rubber specimens at $180^{\circ}C$ caused a slight increase in crosslink density while it did a large decrease in tensile strength and elongation. With aging at high temperature, the formation of carbonyl groups in EPDM molecule chain and formation of sulphoxide crosslink, rather than the crosslink density variation itself, had a large influence on such changes in mechanical property.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.37 no.1
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• pp.17-28
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• 2024

Objectives : This study was conducted to reveal the scientific mechanism of the anti-skin aging activity of Kyung-Ok-Ko(KOK), which is highly useful as a Korean traditional medicine and functional food. Methods : The skin wrinkle and aging inhibitory activity of KOK was confirmed through in vitro experiments of human dermal fibroblast neonatal cell(HDFn) and in vivo of C. elegans, and hairless mouse(SKH-1). Results : The amount of the C-terminus of the collagen precursor in the HDFn cell culture medium treated with KOK using an enzymes-linked immunoassay kit. The group treated with KOK 200㎍/㎖ was a 28.3% increase of collagen precursor compared to the control group. KOK showed inhibitory activity of MMP-1 compared to the control group at a concentration of 200㎍/㎖. In addition, KOK 200㎍/㎖ showed significant inhibitory activity of thermal stress and an oxidative stress compared to the control group in C. elegans. Furthermore, KOK showed a concentration-dependent(100mg/kg and 500mg/kg) anti-wrinkle formation effect in UV-irradiated hairless mouse(SKH-1). Additionally, when KOK was administered to UV-irradiated hairless mice, an increase in procollagen -1 and -3 genes expression was observed, and mmp-1 and mmp-9 genes, which increase collagen decomposition, decreased with the administration of KOK. Conclusions : The skin aging inhibition mechanism of Kyung-Ok-Ko(KOK) is presumed to be achieved through suppressing thermal stress and oxidative stress, suppressing mmp-1 and mmp-9 genes, and increasing procollagen-1 and procollagen-3.

• Proceedings of the Korean Reliability Society Conference
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• 2006.05a
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• pp.27-31
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• 2006

Rubber hoses for automobile radiators are apt to degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under thermal and mechanical loadings. The aging behaviors of the skin part of the hoses due to thermo-oxidative and electro-chemical stresses were experimentally analyzed. Through the thermo-oxidative aging test, it was shown that the surface hardness IRHD(International Rubber Hardness Degrees) of the rubber increased with a considerable reduction of failure strain as the aging time and temperature were large. On account of the penetration of coolant liquid into the skin part the weight of rubber specimens influenced by electro-chemical degradation (ECD) test increased, whereas their failure strain and IRHD hardness decreased. The hardness decreased further as the test site on the hose skin approached to the negative pole.

• Korean Journal of Plant Resources
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• v.33 no.6
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• pp.645-650
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• 2020

The mechanism of anti-aging of fermented jujube (Zizyphus jujuba fruits (ZJF)) was investigated using transgenic daf-16 and mev-1 strains of C. elegans. Jujube extracts fermented for 7 days (F7-ZJF) and 14 days (F14-ZJF) with Laetiporus sulphureus were treated to a NGM agar plate with 10-15 transgenic daf-16 and mev-1 strains of the synchronized age. There was no difference of lifespan between the drug-treated group (7-day fermented ex. (F7-zjf-200 ㎍/mL), 14-day fermented ex. (F14-zjf-200 ㎍/mL)) and the non-treatment group in both daf-16 and mev-1 strains. In the thermal stress experiment, F7-zjf-200 ㎍/mL showed a significant (t = 4.017) activity in thermal stress resistance with a 12% higher survival rate than the control group. In the survival test in H2O2, F7-zjf-200 ㎍/mL and F14-zjf-100 ㎍/mL have significant activity in oxidative stress resistance compared to the control group. This study indicates that life span expand of N2 strain of the jujube extract is related to the regulation of daf-16 and inhibition of mev-1 signal in C. elegans.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.6
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• pp.574-581
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• 1991

Damage in film capacitors has been investigated, using FTIR and ESCA, aiming to elucidate the nature of electrode removal and the possibility of base films to be damaged. Also, tests were conducted to investigate the effect of a long-term thermal aging at elevated temperatures. Unsuccessful clearing or grape-clustering processes can induce a long-term degradation which involves the chemical and morphological changes. Major changes are the oxidation and the decrease in surface crystallinity possibly arising from the corona discharge. An immediate deterioration of BOPP film may occur when the air entrapped between the film layers induces an extensive autocatalytic oxidative degradation. This type of immediate damage may result in a premature failure at an early stage of qualification test. As far as the nature of electrode removal is concerned, a permanent removal of electrode materials was observed in the main erosion area.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.5
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• pp.152-162
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• 2005

Coolant rubber hoses for automobile radiators can be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under the thermal and mechanical loadings. In this study, test analysis was carried out for evaluating the degradation and failure mechanisms of coolant hose materials. Two kinds of EPDM rubber materials applicable to the hoses were adopted: commonly-used ethylene-propylene diene monomer(EPDM) rubbers and EPDM rubbers with high resistance against electro-chemical degradation (ECD). An increase of surface hardness and a large reduction of failure strain were shown due to the formation of oxidation layer for the specimens which had been kept in a high temperature air chamber. Coolant ageing effects took place only by an amount of pure thermal degradation. The specimens degraded by ECD test showed a swelling behavior and a considerable increase in weight on account of the penetration of coolant liquid into the skin and interior of the rubber specimens. The ECD induced material softening as well as drastic reduction in strength and failure strain. However EPDM rubbers designed for high resistance against ECD revealed a large improvement in reduction of failure strain and weight. This study finally established a procedure for reliability analysis and evaluation of the degradation and failure mechanisms of EPDM rubbers used in coolant hoses for automobile radiators.

• Korean Journal of Acupuncture
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• v.31 no.4
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• pp.218-224
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• 2014

Objectives : Zizyphus jujuba fruits(ZJF), a traditional Korean medicine has various biological activities such as anti-inflammatory, anti-oxidative and neuro-protective effects. However, it is still unclear whether ZJF has any biological effect on anti-aging. In this study, we examined the effect of ZJF on lifespan and thermal stress in C. elegans. Methods and Results : ZJF water extracts were fermented for 7 days(F7-ZJF) and 14 days(F14-ZJF) by Laetiporus sulphureus to increase secondary metabolites such as aglycone of flavonoids and terpenoids. In the lifespan assay, ZJF water extracts and fermented ZJF were treated on the agar medium plate with age synchronized egg stage of C. elegans. Treatment of F7-ZJF-$200{\mu}g/mL$ with OP-50 E. coli and F14-ZJF-$200{\mu}g/mL$ with OP-50 E. coli significantly increased life span of C. elegans(N2) at thermal stress condition of $25^{\circ}C$. Moreover mRNA levels of lifespan associated HSP 16.1, HSP 70, and HSF-1 were increased at thermal stress condition of $25^{\circ}C$. However, in the equilibration temperature of $20^{\circ}C$ after stress condition of $35^{\circ}C$ for 2 hr, F-14-ZJF-$200{\mu}g/mL$ treatment decreased the levels of heat shock protein in hsp16.2/GFP C. elegans. Conclusions : Our study indicates that prolong role of fermented-ZJF in C. elegans is mediated by control HSPs production.